The present invention relates generally to speed signal calibration. More particularly, the present invention relates to a method of automatic calibration of speed signal scaling for vehicle electronic systems, such as a cruise control system.
Cruise control systems, among other vehicle systems, process information regarding the speed of a vehicle. In order to measure and determine speed, a vehicle is typically equipped with a vehicle speed sensor operatively coupled to the vehicle""s transmission to monitor the rotational speed of a shaft in the transmission. The speed sensor may include a Hall-effect or variable-reluctance sensor, and generates a vehicle speed sensor (VSS) signal that must be accurately determinable.
The VSS signal comprises a series of pulses which, when used in conjunction with a particular vehicle, has a characteristic xe2x80x9cpulses-per-milexe2x80x9d (ppm) ratio or other comparable ratio. However, these pulse ratios typically vary among automotive systems. Thus, an automotive system using a VSS signal as an input, such as a cruise control module, must be calibrated to the particular vehicle in which it is installed.
In the past, manufacturers of electronic control modules have provided multiple module part numbers to accommodate the various and unique hardware/software calibrations that correspond to a particular ppm ratio of a given speed sensor. These calibrations are typically established at the point of module manufacture. Alternatively, a single module part number may be provided, but this generally results in the calibrations being performed by the purchaser (usually the vehicle manufacturer) of the modules. In this situation, the vehicle manufacturer may end up purchasing and operating expensive, specialized xe2x80x9cend of linexe2x80x9d or field service programming equipment.
It is therefore desirable to provide a calibration method which addresses the aforementioned concerns.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a method for automatically calibrating speed signal scaling for vehicle electronic systems. In an exemplary embodiment of the invention, a method for automatically calibrating a vehicle speed sensor signal input to an electronic control system includes operating a vehicle at a reference speed. A speed signal pulse period, generated by a vehicle speed sensor operatively coupled to the vehicle, is measured. The measured speed signal pulse period is then compared to a stored set of pulse period scalings within the electronic control system. A corresponding pulse period scaling is stored in memory if the measured speed signal pulse period matches one of the stored set of pulse period scalings.
In a preferred embodiment, a system operation flag is set to a first state if the measured speed signal pulse period matches one of the stored set of pulse period scalings. Alternatively, the system operation flag is set to a second state if the measured speed signal pulse period does not match at least one of the stored set of pulse period scalings. The electronic control system is rendered operational if the system operation flag is set to the first state and rendered non-operational if the system operation flag is set to the second state.